1. Field of the Invention
The present invention relates, generally, to telecommunications modems and, in one embodiment, to a method and apparatus for controlling the deactivation of a telecommunications modem to minimize power consumption.
2. Description of Related Art
Cellular communication networks are rapidly becoming a primary infrastructure for enabling communication in today's society. As demand for cellular communications has increased, cellular communication networks have become increasingly prevalent and are providing coverage over larger areas. Rather than just providing a means for voice communications such as personal or business telephone calls, cellular communication networks are now being used for transmitting data and emergency communications. Mobile communications technology has been extended to include mobile communication devices, identified herein as telematics control units (TCUs), installed in vehicles such as automobiles, boats, and the like.
As with a cellular telephone, these TCUs communicate with base stations/sectors in a cellular communication network to provide telematics functionality for the vehicles, which may include, but is not limited to, vehicle tracking and positioning, on-line navigation, emergency “roadside” assistance, remote engine diagnostics, tracking stolen vehicles, entertainment, information services, Internet and e-mail access, automatic emergency transmissions when an accident has occurred, remote door unlocking, telephone and voicemail service, traffic reports, and the like. This telematics functionality is typically provided by a service provider center connected to the TCU through the cellular communication network.
FIG. 1 illustrates an example of a vehicle 10 having a TCU 30 capable of maintaining a connection 34 with a cellular communication network 22 as the vehicle 10 roves through a geographic area served by the cellular communication network 22, or remains stationary at some geographic location within the network 22. It should be understood that a connection, as referred to herein, includes, but is not limited to, voice, multimedia video or audio streaming, packet switched data and circuit switched data connections, short message sequences or data bursts, and paging. The cellular communication network 22 includes a first base station (BS) 12 communicating over sectors 14 and 16, and a second BS 18 communicating over sector 20. A BS is typically comprised of multiple sectors, usually three. Each BS includes a separate transmitter and antenna (transceiver) for each sector, pointed in the direction of the sector. Because a BS can be omni or sectorized, it should be understood that the terms BS and sector may be used interchangeably herein. The BSs are connected to network infrastructure entities including BS controllers (BSC) 24 that may control a cell cluster 26, and communicate with a mobile switching center (MSC) 28. It should be understood that one or more of these network infrastructure entities contain one or more processors for controlling the cellular communications between the TCU 30 and the network 22. The processors include memory and other peripheral devices well understood by those skilled in the art. In addition, a service provider 32 is connected to the mobile switching center 28 for communicating with the TCU 30 through the network 22. Although the service provider 32 is shown as a single block in FIG. 1, it should be understood that the service provider 32 may actually comprise a telematics service system of multiple service centers distributed throughout various geographic areas and networks. The service provider 32 contains one or more telematics system processors for controlling communications with the TCU 30 through the network 22.
As illustrated in the example of FIG. 2, the TCU 30 may include a processor 72, memory 68, antenna 56, TCU transceiver 58, modem 60, Global Positioning System (GPS) receiver 62, and a vehicle interface 66 for controlling vehicle functions such as the door locks, the sound system, and the like. The TCU transceiver may be configured to be compatible with one of more of the following communication protocols: GSM, CDMA, TCS, AMPS, TDMA, FDMA, CDMA, and the like. Although the processor 72 and memory 68 are shown in FIG. 4 in separate blocks, it should be understood that references to TCU herein generally include different types of configurations for processors, memory and other peripheral devices not shown in FIG. 2 but well understood by those skilled in the art.
The TCU 30 and the network communicate using channels. Information in these channels is modulated and demodulated by the modem 22 in accordance with a particular coding scheme or type of cellular communication service. In time division multiple access (TDMA), multiple channels may be communicated at a particular frequency within a certain time window by sending them at different times within that window. Thus, for example, channel X may use one set of time slots while channel Y may use a different set of time slots. In frequency division multiple access (FDMA), multiple channels may be communicated at a particular time within a certain frequency window by sending them at different frequencies within that window.
Code division multiple access (CDMA) is a technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences. It allows a number of TCUs to communicate with one or more BSs, simultaneously using the same frequency. In CDMA, given a space of frequency and time, each channel is assigned a particular orthogonal code such as a Walsh code or a quasi-orthogonal function (QOF). In direct sequence CDMA, the data from each channel is coded using Walsh codes or QOFs and then combined into a composite signal. This composite signal is spread over a wide frequency range at a particular time. When this composite signal is de-spread using the same code used to spread the original data, the original data may be extracted. This recovery of the original data is possible because Walsh codes and QOFs create coded data that, when combined, do not interfere with each other, so that the data can be separated out at a later point in time to recover the information on the various channels. In other words, when two coded sequences of data are added together to produce a third sequence, by correlating that third sequence with the original codes, the original sequences can be recovered. When demodulating with a particular code, knowledge of the other codes is not necessary.
In CDMA systems, signals can be received in the presence of high levels of narrow-band or wide-band interference. The practical limit of signal reception depends on the channel conditions and interference level. Types of interference include those generated when the signal is propagated through a multi-path channel, signals transmitted to and from other TCUs and cellular communication devices in the same or other cell sites, as well as self-interference or noise generated at the TCU. However, noise and interference in the field may require error correction to determine what was actually transmitted.
The CDMA wireless communication system is fully described by the following standards, all of which are published by the TELECOMMUNICATIONS INDUSTRY ASSOCIATION, Standards & Technology Department, 2500 Wilson Blvd., Arlington, Va. 22201, and all of which are herein incorporated by reference: TIA/EIA-95A, published in 1993; TIA/EIA-95B, published Feb. 1, 1999; TIA/EIA/IS-2000, Volumes 1–5, Release A, published Mar. 1, 2000; TIA/EIA-98D, published Jun. 1, 2001; and WCDMA standards 3GPP TS 25.214 V4.2.0 published September 2001, TS25.401 V5.1.0 published September 2001, TS 25.331 V4.2.0 published Oct. 8, 2001, and TR 25.922 V4.1.0 published Oct. 2, 2001.
As noted above, one possible function of the communications available between the service provider and the TCU is to provide emergency “roadside” assistance and automatic emergency transmissions when an accident has occurred. For example, if a vehicle is involved in an accident while the ignition is on and the airbag activates, indicated at time 36 in FIG. 3, the TCU in the vehicle will automatically turn on its modem and initiate a connection session with the network 22 at time 38. Upon successful establishment of the connection, the service provider will attempt to communicate with the TCU by transmitting a connect frame 40. If this connect frame 40 is properly received, the TCU will respond with a data transmission 42 that may include position data from the TCU's GPS device, the vehicle identification number (VID), and other information. This data is provided by the TCU automatically, without need for involvement by the vehicle's occupants, to ensure basic information can be received by the service provider even if the occupants are unable to respond. After receiving the data, the service provider may then transition to voice mode 44, where an attempt will be made by a service provider representative to communicate with the occupants of the vehicle. At a later time, additional data transmissions 46 can be transmitted to the service center, either at preset intervals or upon request by the service center, containing information such as a position update or remote engine diagnostics.
The above-described communication sequence is considered to be an “ignition-on” mode, because the ignition of the vehicle was on at the time the airbag was activated and the emergency communication sequence was initiated. The “ignition-on” designation is preserved even if the vehicle's ignition is shut off as a result of the accident. Typically, whenever the ignition is on, the modem can remain on indefinitely, because there are no power resource issues. When an accident has occurred and a sudden loss of the ignition switch occurs, the modem remains on, listening for connect frames 40 to improve safety.
Communications between the service provider and the TCU may also occur when the ignition is off (“ignition-off” mode). For example, if a person has locked the vehicle's keys inside the vehicle, that person can telephone the service provider, which will initiate a communication to the TCU in the vehicle to unlock the vehicle doors. Other tasks, such as downloading a phone book or updating a preferred roaming list, may also be performed while the vehicle's ignition is off. These ignition-off tasks typically require data transmissions between the service provider and the TCU, and are referred to herein as maintenance calls. Maintenance calls may be triggered by the service provider in the form of a communication such as a short message service (SMS) message transmitted to the TCU. Upon receipt of the SMS message, the TCU can then place a maintenance call to the service provider. Once a connection is established, the TCU and service provider can transmit data and instructions, as necessary, to process the maintenance call and perform the desired maintenance task. Alternatively, the service provider may place a maintenance call directly to the TCU. Maintenance calls may also be triggered by the TCU in the form of an SMS message transmitted to the service provider. Upon receipt of the SMS message, the service provider can then place a maintenance call to the TCU. Alternatively, the TCU may place a maintenance call directly to the service provider. Other protocols may also be employed to place maintenance calls.
The TCU cannot receive nor transmit any messages or calls except during the time that the TCU's cellular transceiver is activated. In the ignition-off mode, the cellular transceiver in the TCU is periodically activated. While active, the transceiver attempts to receive any communications being transmitted by the service provider to the TCU, such as an SMS message directing the TCU to place a maintenance call, or a maintenance call transmitted directly from the service provider. All other components of the TCU remain off, including the modem, to prevent excessive battery drain. One example of the periodic activation of the transceiver is illustrated in FIG. 4. When the ignition is turned off at time 48, the cellular transceiver will stay active (on) for an extended listening period of X hours (see reference character 50), then turn off for Y minutes (see reference character 52), then turn on again for a short listening period of Z minutes (see reference character 54). The Y-Z pattern is then repeated. Note that Y is generally much longer than Z. The repeating Y-Z pattern will continue for a fixed time period such as a predetermined number of days, but if the ignition is not turned on during that time period, the pattern will cease, and the transceiver will not be activated again unless the ignition is first started.
The extended listening period 50 can be considered an override of the typical repeating Y-Z pattern and is provided for customer convenience. For example, if the driver has left the vehicle for an hour, realizes the keys are locked in the vehicle, and notifies the service provider, it would be inconvenient for the driver to have to wait up to Y minutes before the transceiver is activated again and is able to receive a service center SMS message instructing the TCU to place a maintenance call to the service provider to unlock the doors. The repeating Y-Z pattern of transceiver activation is provided to minimize consumption of the vehicle's power budget allocated to the TCU, while still providing periodic opportunities for the TCU to receive communications from the service provider. For example, maintenance calls initiated by the service provider via an SMS message during off-peak hours need not be attended to immediately, so the SMS message can be repeatedly transmitted by the service provider at intervals less than Z minutes to ensure that they will be received by the TCU's transceiver during one of the short listening periods 54.
During the time periods in which the transceiver is active, the service provider may communicate with the TCU in several ways. As described above, the TCU can receive an SMS message from the service provider through the network, instructing the TCU to place a maintenance call. Alternatively, the TCU can receive a callback sequence from the service provider through the network, instructing the TCU to place a maintenance call. A callback sequence is the receipt of two incoming calls within a specified time period. The reason for having these two methods is that in an AMPS network, SMS service is not fully supported across the desired service area, so a callback sequence must be sent. In either case, the TCU will respond by turning on its modem and initiating a connection request back to the service provider to place the maintenance call.
Upon establishment of the connection, data may be received from the service provider instructing the TCU to unlock doors, for example, or receive a preferred roaming list (PRL), which is a list of preferred networks to be used by the TCU when making a connection request. Within the TCU, other information can be updated, such as the phone book, the outgoing call number list used to call the service center, and the like.
During the time periods in which the transceiver is active, the TCU can also receive a maintenance call directly from the service provider. However, before a maintenance call can be received at the TCU, the TCU must detect the start of the maintenance call, and turn its modem on. Once the modem is turned on, data may be received from the service provider instructing the TCU to perform various maintenance tasks.
As described above, during the time periods in which the transceiver is active, the TCU may also transmit an SMS message or a callback sequence to the service provider through the network, instructing the service provider to place a maintenance call. Alternatively, the TCU can also transmit a maintenance call directly to the service provider. However, before a maintenance call can be transmitted from the TCU, the modem in the TCU must be turned on.
Even in the ignition-off mode, when the vehicle is stationary, the connection between the network and the TCU may be poor, because cellular networks are noise limited. For example, if the vehicle is parked at the fringes of the network, the RF parameters in the network change, interference from adjacent channels increases, or the environment surrounding the TCU changes (e.g., a truck has blocked the communication path), data transmissions across the network may not be received properly. When a connection is poor and not all of the information in a data transmission is properly received, the modem in the TCU may remain active and continuously attempt to receive or transmit this information. However, if the connection remains poor and the information is not properly received in a timely manner, the modem may remain on indefinitely. This may be detrimental in the ignition-off mode, when power conservation is important.
Power-saving techniques for turning off modems are known in the art. For example, in data modems not designed for mobile applications, if the modem detects a loss of the carrier tone, the modem immediately turns off, thus saving power. However, in mobile applications, during handoffs between sectors and BSs, the carrier tone will be lost for a brief period of time. If this type of data modem were employed in mobile applications, at every handoff the modem would be turned off and the connection would be dropped, which is an intolerable result.
Similar solutions are known in the art for voice-band data modems. For example, U.S. Pat. No. Re. 34,034, attempts to solve this problem by keeping a voice-band data modem active for a fixed period of time after loss of the voice-band carrier tone, in case the carrier tone quickly resumes, such as in a handoff. If the carrier tone is not detected within the fixed period of time, the modem is then turned off.
CDMA cellular communication systems control the deactivation of the CDMA transceiver, a type of modem, using a frame error rate counter, as established by CDMA system standards. In a CDMA system, data and voice are communicated in 20 ms packets or frames. If frames are not properly received due to a handoff, fading, or other interference, for example, a frame error rate counter increments a count for every frame not properly received. If the counter counts a predetermined number of consecutive bad frames, the modem is turned off and the connection is dropped.
However, in any of the solutions described above, intermittent connection problems that do not result in a loss of carrier tone for the fixed period of time or a loss of a fixed number of consecutive frames may not trigger the deactivation of the modem, resulting in the modem being active for long periods of time and a drain on power budgets. Therefore, a need exists for a method and apparatus for controlling the deactivation of a telecommunications modem, independent of the connection quality, to minimize power consumption.